Researchers have discovered the gene that causes one of the rarest congenital disorders, a disease called FOP that turns muscle and tendons into bone, forming a second skeleton that eventually renders the patient immobile, like a statue.
Fibrodysplasia ossificans progressiva, or FOP, strikes about one in 2 million people -- so rarely that most physicians misdiagnose the disorder, often prescribing treatments that worsen the condition. About 600 patients are known.
The majority of patients become bedridden by their 30s. There is no treatment -- removing the excess bone only makes it grow back faster.
The discovery of the FOP gene could eventually lead to the first treatments for the disease, according to Dr. Frederick S. Kaplan and his colleagues at the University of Pennsylvania School of Medicine.
Their finding, reported Sunday on the website of the journal Nature Genetics, could also lead to new treatments for a variety of other bone diseases that involve either excessive or insufficient bone growth.
"This is a fantastic advance for an absolutely horrible disease," said Dr. Joseph A. Kitterman of UC San Francisco, who was not involved in the research.
FOP is apparent at birth. The patient's big toes, the last segment of the skeleton to form, are unusually short and point outward laterally.
Other symptoms can appear anytime before age 25. The typical first signs are painful swellings on the arm, neck or shoulders. The pain may fade after a few weeks, but the lumps remain.
Mobility progressively decreases. By the teen years, patients usually cannot raise their arms above their heads. As muscles around the lungs convert to bone, breathing becomes more difficult. Trauma, such as bruises, injections and biopsies, accelerate the process.
"This is the only genetic disorder I know of in which one organ is converted into a different one," Kaplan said. "The new bone is totally normal. It is just in the wrong place at the wrong time."
Kitterman, whose step-grandson has the disease, recently surveyed known FOP patients and reported in November in the journal Pediatrics that 87% of them were initially misdiagnosed.
Nearly 50% of them, moreover, received permanent injuries from inappropriate treatment. Kitterman's grandson, like many others, received cancer chemotherapy. Kaplan cited the case of one girl whose arm was amputated because doctors thought she had cancer.
